1. Field of the Invention
The present invention relates to a specimen holder which is used for observing the cross section of a wafer specimen with a scanning electron microscope in order to judge whether or not there is a defect in a manufactured wafer and a method for controlling the specimen holder, and more particularly, to a specimen holder and a method for controlling the same, which can easily and rapidly mount a specimen and fasten the specimen in order to allow observation of the specimen by joining a body and a stand of the specimen holder together.
2. Background Art
In general, a process of manufacturing a semiconductor device repeatedly carries out a diffusion process, an oxidation process, a metallization process, and so on. Therefore, various kinds of materials, for instance, insulation films, such as a metal film of Al, Ti, W or others, a nitride film, an oxide film or others, on a wafer.
In the case that there is something wrong with some of the multiple laminated films, because the semiconductor device formed by the follow-up process may have a malfunction, technology to exactly and effectively analyze and verify such a malfunction is needed.
Due to an integration of the semiconductor device, the semiconductor device may have a malfunction by a minute cause, and it aggravates difficulty in analyzing the malfunction which may occur in the semiconductor device.
A transmission electron microscope (TEM) or a scanning electron microscope (SEM) may be used in order to analyze and verify the film or pattern formed on the wafer.
The transmission electron microscope is an apparatus for obtaining an image by electron beams transmitted through a specimen and analyzing a crystal structure of a phase by a diffraction pattern obtained through the diffracted electron beams.
The scanning electron microscope discharges a flow of electrons having acceleration energy (normal to 30 KV) using an electron gun and forms a focus of electron beams using various electromagnetic lenses, apertures and so on. A user scans the formed electron beams to a target sample to be observed and controls magnification. When secondary electrons, back scatter electrons, transmission electrons, characteristic X-rays formed from the target sample are detected, the user can observe the cross section of the target sample and analyze characteristics of the cross section of the target sample.
The scanning electron microscope basically includes an electron column, a sample chamber, a vacuum pump, a vacuum gauge, various controlling parts for controlling the electron column, and an image processing system. The electron column includes an electron gun, a lens, an aperture, a signal detector, and others, and the vacuum pump has a structure to form an ultra-high vacuum to remove various obstacles, such as scattering, discharge, and pollution of the electron beams by gas molecules in the air.
As the electron gun of the scanning electron microscope, there are thermionic emission guns, cold cathode field emission (CFE) guns, schottky field emission (SFE) guns, and others, and the scanning electron microscope is greatly varied in performance and structure according to kinds of the electron gun. Generally, the scanning electron microscope using the CFE gun and the SFE gun is called an FE-SEM (Field Emission Scanning Electron Microscope), and the scanning electron microscope using the thermionic emission gun is called a normal SEM.
The lens is divided into two kinds, namely, a condenser lens and an objective lens. The condenser lens first condenses electron beams emitted from the electron gun and forms the first focus, controls probe current arriving at the sample, and generally one or two condenser lenses are used. The objective lens is to accurately focus the electron beams formed in the condenser lens on the target sample, and has a scanning coil for controlling a scanning area of the electron beams scanned to the target sample and forming magnification.
The aperture is divided into a fixed type aperture and a variable type aperture which can vary a size of a hole. A plurality of the fixed type apertures are located inside the electron column by use according to design structures of manufacturers. The variable type aperture is generally called an objective lens aperture and is located on the objective lens in order to control a current amount of beams introduced into the objective lens, to regulate a size of the focus, and to reduce various aberrations.
When electron beams having acceleration voltage according to analysis purposes are scanned to the target sample from the electron column after being focused and reduced, backscattered electron (BSE) signals of the secondary electrons and incident beams are generated according to peculiar characteristics of the target sample. The signals are collected and amplified by the secondary electron detector or a BSE detector and contrast and brightness are applied to the signals according to signal quantities in order to process the image, so that the user can magnify and observe a morphological image of the cross section of the target sample. Moreover, if characteristic X-rays of elements generated when the incident beams collide with the target sample are detected (EDXS), qualitative and quantitative analysis data can be obtained. Furthermore, if the transmission electron detector (STEM) is attached according to use purpose, various applications such as a structure analysis of the target sample can be made.
FIG. 1 is a view showing an out-lens and semi-in-lens type FE-SEM, and FIG. 2 is a view showing an in-lens type FE-SEM to which the present invention is applicable. The FE-SEM is utilizable in various fields, such as semiconductors, displays (LCDs, LEDs, OLEDs, and others), the rays of the sun, various Nano-materials, biology, medical science, electronics, machineries, physics, chemical materials, various materials, and material studies. The FE-SEM illustrated in FIGS. 1 and 2 includes an electron source 31, a beam monitor aperture 32, a first condenser lens 33, an air lock valve 34, an objective movable aperture 35, a second condenser lens 36, a deflection coil 37, an EXB 38, an objective lens 39, a secondary electron detector 45, and others. The In-lens type FE-SEM of FIG. 2 further includes an objective lens coil 40 and a beam blanking 41, and may further include a dark field STEM detector 42, a bright field aperture 43, and a bright field STEM detector 44. The out-lens and semi-in-lens type FE-SEM illustrated in FIG. 2 allows the user to observe samples of a large size because a specimen 11 is located below the objective lens and a working distance is long, but is deteriorated in image resolving power because the working distance is long. On the contrary, the In-lens type FE-SEM of FIG. 3 to which the present invention is applied allows the user to observe only samples of a small size because the specimen 11 is located inside the objective lens and the working distance is short, but can obtain an image of ultra-high resolving power.
In the meantime, as illustrated in FIGS. 3 and 4, a method of using a set screw 12 in order to fix the specimen. That is, the specimen 11 can be fixed to the holder in such a manner that the specimen 11 is tightened after a spacer 11a is put between the specimen 11 and the set screw 12. However, such a method has several problems in that it is difficult to properly regulate height or horizontally of the specimen 11 fixed on the holder because the set screw 12 is very small, in that there is a fear of missing the set screw 12 and the spacer 11a, and in that the set screw 12 may be easily worn out.
In the meantime, as shown in FIG. 5, there is a conventional method of fixing the specimen 11 using tension of a leaf spring 14. That is, when the specimen 11 is mounted on the holder and a latch hole 13 moves backward, a clamp 15 is pushed backward and the specimen 11 is fixed to the holder by tension of the leaf spring 14. However, such a conventional method has several problems in that the specimen 11 may be separated from the holder because tension of the leaf spring 14 gets weaker, and in that it is difficult to obtain a clear image due to occurrence of an image drift. Moreover, the conventional method is restricted in utilization because it has a structure that it is difficult to fix a thin specimen 11.
Therefore, a development of a specimen holder which can simply and easily fix the specimen and obtain a clear and clean image is required.